python庫skimage 繪製直方圖；繪製累計直方圖；實現直方圖匹配(histogram matching)

繪製直方圖

from skimage import exposure
# 繪製彩色圖像的c通道的直方圖
img_hist, bins = exposure.histogram(img[..., c], source_range='dtype')
# 以第c行第i列的形式繪製歸一化直方圖
axes[c, i].plot(bins, img_hist / img_hist.max())

繪製累積直方圖

from skimage import exposure
img_cdf, bins = exposure.cumulative_distribution(img[..., c])
axes[c, i].plot(bins, img_cdf)

直方圖匹配(histogram matching)

含義：使源圖像的累積直方圖和目標圖像一致

from skimage.exposure import match_histograms
# 參數1：源圖像；參數2：目標圖像；參數3：多通道匹配
matched = match_histograms(image, reference, multichannel=True)

實驗：直方圖匹配效果

"""
==================
Histogram matching
==================

This example demonstrates the feature of histogram matching. It manipulates the
pixels of an input image so that its histogram matches the histogram of the
reference image. If the images have multiple channels, the matching is done
independently for each channel, as long as the number of channels is equal in
the input image and the reference.2

Histogram matching can be used as a lightweight normalisation for image
processing, such as feature matching, especially in circumstances where the
images have been taken from different sources or in different conditions (i.e.
lighting).
"""

import matplotlib.pyplot as plt

from skimage import data
from skimage import exposure
from skimage.exposure import match_histograms

reference = data.coffee()
image = data.chelsea()

matched = match_histograms(image, reference, multichannel=True)

fig, (ax1, ax2, ax3) = plt.subplots(nrows=1, ncols=3, figsize=(8, 3),
                                    sharex=True, sharey=True)
for aa in (ax1, ax2, ax3):
    aa.set_axis_off()

ax1.imshow(image)
ax1.set_title('Source')
ax2.imshow(reference)
ax2.set_title('Reference')
ax3.imshow(matched)
ax3.set_title('Matched')

plt.tight_layout()
plt.show()


######################################################################
# To illustrate the effect of the histogram matching, we plot for each
# RGB channel, the histogram and the cumulative histogram. Clearly,
# the matched image has the same cumulative histogram as the reference
# image for each channel.

fig, axes = plt.subplots(nrows=3, ncols=3, figsize=(8, 8))


for i, img in enumerate((image, reference, matched)):
    for c, c_color in enumerate(('red', 'green', 'blue')):
        img_hist, bins = exposure.histogram(img[..., c], source_range='dtype')
        axes[c, i].plot(bins, img_hist / img_hist.max())
        img_cdf, bins = exposure.cumulative_distribution(img[..., c])
        axes[c, i].plot(bins, img_cdf)
        axes[c, 0].set_ylabel(c_color)

axes[0, 0].set_title('Source')
axes[0, 1].set_title('Reference')
axes[0, 2].set_title('Matched')

plt.tight_layout()
plt.show()

實驗輸出